A typical aircraft has landing gear comprising a plurality of undercarriages which support the aircraft when it is on the ground. The undercarriages are used to control the movement of the aircraft during ground maneuvers such as landing, taxiing and take off. Some of the undercarriages have braking wheels which are operable to provide a braking force to decelerate the aircraft when a braking torque is applied by a set of brakes.
In use, the braking torque generated by each braking wheel of the aircraft may vary, for example due to differences in brake gain (the ratio of the actual braking torque to the clamping force used to control the braking torque). Variations in brake torque across the braking wheels may cause variations in loading of the undercarriages, therefore increasing the design requirements and also the weight of the aircraft. Variations in brake torque may also lead to asymmetric braking (the generation of uneven braking forces either side of the aircraft center-line) resulting in a net yaw moment which may need to be corrected by a pilot or control system, increasing pilot and control system workload.
In use, the brakes may also heat up at different rates, for example due to variations in brake gain, resulting in temperature scatter (temperature differentials between the brakes). Temperature scatter may lead to increased aircraft turn-around time or TAT (the time for which an aircraft is grounded before a flight) and increased wear rates of brake system components.
Controlling temperature scatter and variations in brake torque may be particularly difficult in failure modes, where the ability of a braking system to function optimally may be impaired.
It is therefore desirable to provide a braking system for an aircraft which addresses these problems and allows an aircraft to perform ground maneuvers with maximum efficiency within the available performance envelope, particularly in failure modes when performance may be reduced.